1. Field of the Invention
The present invention relates to a water repellent coating composition having excellent water repellency, antisnow-sticking and weatherability, coating films and coated articles using such a water repellent coating composition.
The water repellent coating composition can be used widely including construction, civil engineering, etc. because of high water repellency, antisnow- or antiice-sticking properties, and weatherability.
The present invention is applicable to prevention of leakage of water or antisnow- or antiice-sticking surface treatment for various antennae, e.g., antennae for satellite communication and satellite broadcasting, antenna domes for communication, antennae for flight control, Yagi antennae and the like. Also, the present invention can be applied to reflector plates for radars and radiotelescopes, iron towers, cables, transmission lines, constructions and facings thereof, such as houses, buildings, roofs or outer walls thereof, vehicles such as electric cars, trains, automobiles, ships, airplanes, jigs for civil engineering machines, ventilation or exhaustion outlets of chimneys and stoves. The water repellent coating composition of the present invention can be provided in the form of a dispersion or as contained in a spray can.
2. Description of Related Art
Development of water repellent coating compositions having excellent water repellency, antisnow- or antiice-sticking property, and weatherability will enable realization of antennae, cables, towers, roofs and the like which are resistant to snow-sticking by coating such coating compositions thereon and will also find application to a wide such coating compositions will find their way into many uses including coating of jigs for civil engineering machines and the like. However, many of the conventional water repellent coating compositions or water repellent coating materials have initial contact angles of not higher than 140 degrees, which decrease considerably during use of the coated article, leading to loss of water repellency. There has been known a technology in which fluororesin powder is electro-deposited on the surface of a substrate to endow it with water repellency. In this technology, the electro-deposition is impossible on substrates such as constructions or articles outdoors so that its application has been limited. Also, it has been proposed to use fluororesin powder having a specified particle diameter in order to endow water repellency. However, the characteristics of powder are not defined by particle diameter alone but generally depend on various other factors and, hence, it is practically difficult to obtain deposition with a high performance by a mere control of the particle diameter of powder. Recently, a water repellent coating composition has been proposed which comprises a matrix resin such as an acrylic-silicone resin and a low molecular weight polytetrafluoroethylene (PTFE) powder with a molecular weight of 500 to 20,000 which is fluorinated to the ends thereof dispersed in the matrix resin Japanese Patent Application Laying-open No. 6-122838 (1994). The coated surface obtained with this coating composition had a contact angle of 140 degrees (.degree.) or more and was considered to have excellent water repellency.
However, use of specific low molecular weight PTFE having fluorinated to the ends thereof in the water repellent coating composition mandates a special manufacturing process, which makes it difficult to produce the coating composition on a large scale, thus leading to high costs. Further, because of its low molecular weight, the water repellent powder used in the conventional water repellent coating composition has a relatively low melting point; although the melting point itself distributes in a certain range, the representative value thereof is 230.degree. C. As a result, the conventional water repellent coating composition is weak to heat.